U.S. patent number 4,053,833 [Application Number 05/553,780] was granted by the patent office on 1977-10-11 for contactless test method for integrated circuits.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to David Green, Robert M. Handy, Paul R. Malmberg, Donald F. Stoneburner.
United States Patent |
4,053,833 |
Malmberg , et al. |
October 11, 1977 |
Contactless test method for integrated circuits
Abstract
A method is provided for contactless testing of an integrated
circuit by fabricating, integrally with the integrated circuit, at
least one and preferably a plurality of conductive semiconductor
elements that are electrically connected between power and/or
signal sources and inputs to the integrated circuit, and that are
adapted to electrically conduct when exposed to a radiation beam.
The conductive elements are selectively exposed by at least one
radiation beam, such as an electron or light beam, to cause the
conductive elements to electrically conduct and supply desired
electrical inputs at the connected inputs of the integrated
circuits; and the electrical responses of at least a segment of the
integrated circuit to said electrical input are measured to
determine whether said circuit segment possesses specified
electrical characteristics. The integrated circuit can thus be
selectively and sequentially tested by segments and modules. After
testing, the conductive semiconductor elements are preferably
disconnected from the integrated circuit, and the integrated
circuit selectively connected electrically while accommodating and
passivating defective components and modules of the circuit.
Inventors: |
Malmberg; Paul R. (Pittsburgh,
PA), Handy; Robert M. (Phoenix, AZ), Stoneburner; Donald
F. (Monroeville, PA), Green; David (Painted Post,
NY) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
27033005 |
Appl.
No.: |
05/553,780 |
Filed: |
February 27, 1975 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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441924 |
Feb 12, 1974 |
3956698 |
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Current U.S.
Class: |
324/754.22;
324/762.02 |
Current CPC
Class: |
G01R
31/303 (20130101) |
Current International
Class: |
G01R
31/28 (20060101); G01R 31/302 (20060101); G01R
031/26 (); G01R 015/12 () |
Field of
Search: |
;324/158R,73R,158D,158T
;29/574 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Donath, W. E.; "Testing of Integrated Circuits"; IBM Tech. Disc.
Bull., Jan. 1966; p. 1166..
|
Primary Examiner: Rolinec; Rudolph V.
Assistant Examiner: Karlsen; Ernest F.
Attorney, Agent or Firm: Menzemer; C. L.
Government Interests
GOVERNMENT CONTRACT
This invention was made in the course of or under U.S. Government
Contract No. F 33615-C-1335.
Parent Case Text
RELATED APPLICATIONS
The present application is a continuation-in-part application of
copending application Ser. No. 441,924, filed Feb. 12, 1974, now
U.S. Pat. No. 3,956,698.
Claims
What is claimed is:
1. A method of contactless testing an integrated circuit
comprising:
A. fabricating integrally with an integral circuit to be tested a
plurality of conductive semiconductor elements with different
resistance values and having outputs electrically connected to at
least one input to said integrated circuit, each conductive
semiconductor element (i) having an input adapted for electrical
connection to an electrical source and an output electrically
connected to at least one input of said integrated circuit, and
(ii) being adapted to electrically conduct when exposed to a
radiation beam and supply at a connected input or inputs to said
integrated circuit a desired electrical input;
B. connecting inputs of said conductive semiconductor elements to
at least one electrical source;
C. selectively exposing at least one said conductive semiconductor
element with a radiation beam to cause said conductive element to
electrically conduct and supplying a plurality electrical inputs of
different voltage levels at the connected inputs of said integrated
circuit from the electrical source; and
D. measuring electrical responses of at least a segment of the
integrated circuit to said electrical input to determine whether
said circuit segment possesses specified electrical
characteristics.
2. A method of contactless testing an integrated circuit
comprising:
A. fabricating integrally with an integrated circuit to be tested
at least one conductive semiconductor element (i) having an input
adapted for electrical connection to at least one input of said
integrated circuit, (ii) being adapted to electrically conduct when
exposed to a radiation beam and supply at the connected input to
said integrated circuit a desired electrical input, and (iii)
forming one radiation activated thyristor and one radiated
activated transistor electrically connected in parallel in at least
one conductive semiconductor element;
B. connecting inputs of said conductive semiconductor elements to
at least one electrical source;
C. selectively exposing at least one said conductive semiconductor
element with a radiation beam to cause said conductive element to
electrically conduct and supply a desired electrical input to the
connected inputs of the integrated circuit from the electrical
source; and
D. measuring electrical responses of at least a segment of the
integrated circuit to said electrical input to determine whether
said circuit segment possesses specified electrical
characteristics.
3. A method of contactless testing an integrated circuit
comprising:
A. fabricating integrally with an integrated circuit to be tested
at least one conductive semiconductor element (i) having an input
adapted for electrically connected to at electrical source and an
output electricaly connected to at least one input of said
integrated circuit, (ii) being adapted to electrically conduct when
exposed to a radiation beam and supply at the connected input to
said integrated circuit a desired electrical input; and (iii)
forming at least two transistors in close proximity in at least one
conductive semiconductor element;
B. connecting inputs of said conductive semiconductor elements to
at least one electrical source;
C. selectively exposing at least one said conductive semiconductor
element with a radiation beam to cause said conductive element to
electrically conduct and supply a desired electrical input to the
connected inputs of the integrated circuit from the electrical
source; and
D. measuring electrical responses of at least a segment of the
integrated circuit to said electrical input to determine whether
said circuit segment possesses specified electrical
characteristics.
4. A method of contactless testing an integrated circuit
comprising:
A. fabricating integrally with each segment of an integrated
circuit to be tested at least one conductive semiconductor element
(i) having an input adapted for electrical connection to an
electrical source and an output electrically connected to at least
one input of said segment, (ii) being adapted to electrically
conduct when exposed to a radiation beam and supply at the
connected input to said segment a desired electrical input; (iii)
forming a plurality of conduct semiconductor elements with
different resistance values and having outputs electrically
connected to at least one input to said integrated circuit;
B. connecting inputs of said conductive semiconductor elemnts at
least one electrical source;
C. selectively exposing at least one conductive semiconductor to a
radiation beam to cause said conductive element to a conductive
element to electrically conduct and supplying a desired electrical
signal to a plurality of electrical inputs of different voltage
levels at a connected input or inputs of said integrated
circuit;
D. measuring electrical responses of said segment of the integrated
circuit to said electrical input to determine whether said segment
possesses specified electrical characteristics; and
E. repeating steps C and D separately with respect to at least one
other said segment of the integrated circuit.
5. A method of contactless testing an integrated circuit
comprising:
A. fabricating integrally with each segment of an integrated
circuit to be tested at least one conductive semiconductor element
(i) having an input adapted for electrical connection to an
electrical source and an output electrically connected to at least
one input of said segment (ii) being adapted to electrically
conduct when exposed to a radiation beam and supply at the
connected input to said segment a desired electrical input; and
(iii) forming one radiation activated thyristor and one radiated
activated transistor electrically connected in parallel in at least
one conductive semiconductor;
B. connecting inputs of said conductive semiconductor elements at
least one electrical source;
C. selectively exposing at least one conductive semiconductor to a
radiation beam to cause said conductive element to electrically
conduct and supply a desired electrical signal to the connected
inputs of one said segment of the integrated circuit from the
electrical source;
D. measuring electrical responses of said segment of the integrated
circuit to said electrical input to determine whether said segment
possesses specified electrical characteristics; and
E. repeating steps C and D separately with respect to at least one
other said segment of the integrated circuit.
6. A method of contactless testing an integrated circuit
comprising:
A. fabricating integrally with each segment of an integrated
circuit to be tested at least one conductive semiconductor element
(i) having an input adapted for electrical connection to an
electrical source and an output electrically connected to at least
one input of said segment, (ii) being adapted to electrically
conduct when exposed to a radiation beam and supply at the
connected input to said segment a desired electrical input, and
(iii) forming at least two transistors in close proximity in at
least one conductive semiconductor element;
B. connecting inputs of said conductive semiconductor elements at
least one electrical source;
C. selectively exposing at least one conductive semiconductor to a
radiation beam to cause said conductive element to electrically
conduct and supply a desired electrical signal to the connected
inputs of one said segment of the integrated circuit from the
electrical source;
D. measuring electrical responses of said segment of the integrated
circuit to said electrical input to determine whether said segment
possesses specified electrical characteristics; and
E. repeating steps C and D separately with respect to at least one
other said segment of the integrated circuit.
Description
FIELD OF THE INVENTION
The present invention relates to the testing of integrated circuits
and other micro-miniature electronic components without the use of
mechanical test probes.
BACKGROUND OF THE INVENTION
Integrated circuit technology is producing circuits with increasing
complexity and component density. Elements as small as 1 and 2
microns in size can be produced using an electron image projection
system described in U.S. Pat. No. 3,679,497, granted July 25, 1972.
As a result, memory cells as small as 1.2 .times. 10.sup.-6
cm.sup.2 and gate areas as small as 4 .times. 10.sup.-6 cm.sup.2
are achievable, which should permit fabrication of an entire 20,000
gate logic, 256,000 bit memory computer on a 1 cm.sup.2
semiconductor wafer.
One of the severely limiting factors on such microminiaturization
is the testing procedure necessary to the circuit fabrication. It
is practically impossible to manufacture a defect-free complex
integrated circuit. Thus, during and/or after fabrication, the
individual segments and modules of the circuit must be separately
tested to determine whether the electrical characteristics are in
accord with the design values within allowable tolerances. At
present, such testing is done with mechanical probes which
physically contact the input and output electrodes of the
individual segments and modules so that a test device can measure
the input and/or output voltage and current.
The problem is that the smallest area of metal which can be
satifactorily contacted mechanically with a fine wire probe system
is about 75 .times. 75 microns -- larger than the individual logic
gates of a high density integrated circuit. The test points become
too numerous and too closely spaced to be mechanically contacted
when the circuit is micro-miniaturized. Testing by mechanical probe
thus places a limit on the density of the circuit unrelated to
fabrication capabilities and limitations.
Further, testing by mechanical probes can cause severe damage to
the integrated device. Although fine wire test probes may seem very
flexible to a human observer, they are very stiff and heavy
relative to the fine structure of integrated circuits. Mechanical
probes (i) can contaminate and abrade the device surfaces so that
subsequent fabrication steps, e.g. final metalization, cannot be
effectively accomplished, and (ii) can exert high localized forces
and introduce localized stresses so that active regions of the
device are dislocated and distorted. In addition, a mechanical
probe can score electrodes and damage oxide layers. Quality control
and quantitative yields can, therefore, be increased by eliminating
mechanical probes.
A finely-focused electron beam in a vacuum chamber can in some
instances be used as a contactless probe in the testing of planar
electron devices, and particularly integrated circuits, in place of
mechanical contact probes. Under control from a digital computer,
the electron beam can be very accurately addressed to coordinate
locations on an integrated circuit at high speed. However, the use
of an electron beam for contactless testing of integrated circuits
is very restricted in its applications.
The use of multiple electron beams in contactless testing is
virtually impossible. The apparatus for such multiple beams is
bulky and requires separate control of the beams. Further,
tremendous difficulty is encountered in isolation of the beams and
in accurately addressing the beams relative to each other. As a
result, only a single small-dimensioned electron beam is
practicable for contactless testing. However, a single electron
beam cannot hold both an input signal at a desired level at one
address and also go to other coordinate addresses to, for example,
set other input conditions or test the electrical characteristics
of the circuit. Moreover, testing circuits with an electron beam
presents difficulties in deenergizing or isolating circuits not
being tested while energizing the particular segment or module
under test.
The present invention overcomes these difficulties and
disadvantages. It permits one or more input conditions to be set by
a radiation beam and held at a desired level, while other input
conditions are set preferably by a radiation beam and the
electrical characteristics are tested preferably by an electron
beam. It permits contactless testing of a single circuit module
while the other circuit modules on an integrated circuit chip are
maintained in a deenergized condition.
SUMMARY OF THE INVENTION
A method is provided for contactless testing of integrated circuits
and particularly selective and sequentially testing of segments and
modules of a high density integrated circuit. Specifically, small
circuit or component segments and preferably modules (nodes) of an
integrated circuit are selectively energized, and preferably also
deenergized, with at least one radiation beam so that a large
number of circuit segments or modules and/or a large number of
inputs and outputs of a particular circuit segment or module can be
rapidly tested without mechanical damage to the circuit.
Thereafter, the good circuit modules or segments are preferably
selectively connected in large scale integrated circuits by
computer-derived wiring techniques.
The integrated circuit to be tested, preferably in modules (nodes),
has fabricated integrally therewith at least one conductive
semiconductor element with an input adapted for electrical
connection to an electrical power or signal source and an output
electrically connected to at least one input of the integrated
circuit. Preferably, where the circuit is fabricated in modules, at
least one semiconductor conductive element is provided for each
power and each signal input to each module.
Each conductive semiconductor element is normally electrically
nonconductive but is adapted to be electrically conductive when
exposed to a radiation beam, such as an electron or light beam, and
supply at the connected input to said integrated circuit a desired
electrical input from said electrical source. Said conductive
semiconductor element may require continued exposure to the
radiation beam to maintain electrical conductivity between an
electrical source and the connected input of the integrated
circuit. Preferably, however, said conductive semiconductor
elements are adapted to switch from a blocking state to a
conductive state and maintain in a conductive state on limited
irradiation, so that only a short duration exposure to a radiation
beam is needed to establish the test conditions.
Thereafter, the inputs of the conductive semiconductor elements are
connected to power and signal electrical sources, respectively. The
conductive elements are then selectively exposed by at least one
radiation beam, preferably from a standard electron microscope or a
conventional gas laser, to cause the exposed conductive elements to
electrically conduct and selectively supply the desired electrical
power and electrical signals at the connected inputs to the
integrated circuit. Electrical responses of at least segments of
the integrated circuit to said electrical inputs are then
selectively measured to determine whether said segments possess
specified electrical characteristics.
Preferably, a single electron beam is used to expose the conductive
semiconductor elements to provide the electrical inputs to the
connected inputs of the integrated circuit as well as to measure
the electrical characteristics of the integrated circuit in
response to the electrical inputs. Alternatively, the electrical
characteristics of the circuit are preferably measured with an
electron beam, while one or more light beams (which do not
interfere with the precision addressing of the electron beam) are
used to selectively adapt the conductive elements to electrically
conduct.
Where the integrated circuit is fabricated in modules, the modules
can be and are preferably selectively and sequentially supplied
with electrical power and signal inputs by selective exposure of
the conductive semiconductor elements. Accordingly, the electrical
responses of the modules can be separately measured to determine
whether each module possesses the specified electrical
characteristics based on the inputs.
In certain embodiments, each conductive semiconductor element is
preferably fabricated so that it comprises a radiation activated
thyristor and radiation activated transistor in parallel. By this
arrangement, the desired electrical inputs supplied to the
integrated circuit can be rendered electrically nonconductive as
well as conductive without continued exposure of the conductive
element with a radiation beam, thereby providing for more rapid
testing of the integrated circuit. Alternatively, multiple power
and signal inputs can be simultaneously supplied to the integrated
circuit by fabricating at least some of the conductive elements as
radiation activated transistors in close proximity.
Where multiple signal or power levels are needed at one input to
test a given segment or module, it is preferred that a plurality of
conductive semiconductor elements, with different resistance values
corresponding to the desired input levels, be fabricated along with
the integrated circuit and electrically connected to one input of
said integrated circuit. The segment or module can thus be tested
at the desired input levels by sequential exposure of the
conductive elements, or combinations thereof, while the measurement
of electrical responses of said segment or module is continued to
determine whether the segment or module possesses specific
electrical characteristics based on the electrical inputs.
In any case, the conductive semiconductor elements are preferably
disconnected from the integrated circuit after testing. Thereafter,
the segments or modules which test good are selectively
electrically connected, and/or the segments or modules which test
defective are selectively electrically disconnected from the
integrated circuit.
Other details, objects and advantages of the invention will become
apparent as the following description of the presently preferred
embodiments and presently preferred methods of performing the
invention proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring to the drawings, the present preferred embodiments of the
invention and present methods of performing the invention are
illustrated, in which:
FIG. 1 is a circuit diagram showing means for performing the
present invention;
FIG. 2 is a circuit diagram showing alternative means for
performing the present invention;
FIG. 3 is a circuit diagram showing second alternative means for
performing the present invention;
FIG. 4 is a circuit diagram showing third alternative means for
performing the present invention;
FIG. 5 is a circuit diagram showing fourth alternative means for
performing the present invention;
FIG. 6 is a circuit diagram showing fifth alternative means for
performing the present invention; and
FIG. 7 is a circuit diagram showing sixth alternative means for
performing the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a circuit diagram is shown of an integrated
circuit made utilizing the present invention. The integrated
circuit preferably of high density is built, including integrated
segments or modules A and B, preferably by use of the electron
image projection system. Modules A and B are any integrated circuit
modules requiring testing, e.g. transistor-transistor logic
circuits and transistor-diode logic circuits. Segments or modules A
and B are typically circuit segments, but in appropriate
applications may be individual electrical components and devices.
As part of the integrated circuit structure, modules A and B are
provided with power input leads 10 and 11, respectively, signal
input leads 23 and 24, respectively, and output leads 12 and 13,
respectively. The modules are designed to be supplied with
electrical power through leads 10 and 11 and leads 15 and 16 from
common supply bus 14; but at the test stage as hereinafter
described, leads 15 and 16 are not yet electrically connected to
the circuit modules. The electrical signal input is typically
supplied to the modules through leads 23 and 24 from external
contact pads or other parts of the integrated circuit.
Also fabricated as part of the integrated circuit structure are
conductive semiconductor elements 17 and 18 having output leads 19
and 20, respectively, electrically connected typically ohmically to
power input leads 10 and 11 of circuit modules A and B,
respectively. Conductive elements 17 and 18 have base regions 25
and 26, respectively, of configurations so that the conductive
elements, which are normally electrically nonconductive and
blocking, are adapted to be electrically conductive on selective
exposure to radiation beam 27 typically of fine dimensions of any
suitable radiation, such as electron or light radiation. Conductive
elements 17 and 18 also have input leads 21 and 22 electrically
connected to the common power supply bus 14.
Conductive semiconductor elements 17 and 18 are typically
conventional electron or light radiation activated thyristors with
a four-layer structure. The radiation exposure in turn changes the
electrical mode of each device from a high impedance blocking state
to a low impedance conducting state. The conductive element
preferably remains in the low impedance state so long as the supply
current is applied without continuing exposure by the radiation
beam.
Alternatively, conductive semiconductor elements 17 and 18 are
conventional electron or light radiation activated transistors with
a three-layer structure and preferably a relatively long turn-off
time. Such transistor continues in the conduction mode so long as
radiation is continued, which can be done with one or more light
beams without interfering with the testing of the integrated
circuit with an electron beam. Preferably, however, such
transistors are adapted to reach a saturation condition on exposure
to an electron beam so that substantial stored charge remains in
the base region at the end of the exposure and a long turn-off time
results. The long turn-off time enables the transistor to remain in
a conducting state long enough for an electron beam to be deflected
elsewhere in the circuit to turn-on other inputs and measure the
electrical characteristics of the circuit.
After fabrication of the integrated circuit, conductive
semiconductor elements 17 and 18 are selectively exposed to
radiation beam 27 to cause the elements to switch to a conducting
state and selectively supply the desired electrical input signal to
the circuit module A or B through input lead 10 or 11. Beam 27 is
preferably a fine-dimensioned radiation beam projected by a
standard scanning electron microscope so that the beam can be
accurately addressed and deflected at high speed to various
locations within a relatively large scan field. Alternatively, beam
27 is preferably one or more fine-dimensioned light beams
preferably projected by commercially available collimated gas
lasers so that the desired electrical input signals can be
maintained without interfering with the electron beam that measures
the electrical response of the integrated circuit to the electrical
inputs. In this connection, it should be noted that the operation
of each conductive element involves a multiplication by many times
of the radiation energy. That is, the electron or light beam energy
is many times less than the resulting electrical current from the
conductive semiconductor element. This multiplication results from
the fact that an electron or photon (7/8 3.5 ev) bombarding
conductive element produces a large number of electron-hole pairs
and in turn a large number of carriers. Typical values for incident
beam energy and resulting electrical current are 10.sup.4 volts and
10.sup.-8 amperes. While only a fraction of the carriers are
conductive from the conductive element because of recombination
(e.g. 5%), the gain factor is considerably higher than
base-collector current gain of the conductive element, which also
multiplies the current outputs.
Then, the circuit modules A and B may be selectively tested by
measuring the current or voltage response in external output of
input leads to the electrical supply at the electrical inputs,
which typically includes in addition to the power input a signal
input through lead 23. It should be emphasized that the electrical
response of the module can be tested by measuring the total current
supplied through bus 14 because the module being tested is
substantially isolated from the remainder of the circuit, except
for desired input signals through leads 23, and in turn leakage
currents through other parts of the circuit cannot obscure the load
current variations by the module being tested. Preferably, however,
the electrical characteristics are measured by an electron beam
utilizing known techniques, see e.g. U.S. Pat. No. 3,549,999.
After testing, the output leads 19 and 20 from the conductive
semiconductor elements 17 and 18 to input leads 10 and 11 of the
circuit modules are preferably disconnected; and preferably in
immediate sequence, the leads 15 and 16 are formed to ohmically
connect the inputs 10 and 11 to the supply bus 14 if desired.
Preferably, these steps are accomplished by (i) selective
metalization with standard vapor or sputter deposition techniques
to deposit metal layers in the areas of the integrated circuit
where leads 15 and 165 are to be formed, and (ii) photo- or
electro-masking and selective etching of the newly formed metal
layers and the leads 19 and 20. The conductive semiconductor
elements used in testing are thereby disconnected and the input
power supply leads concurrently connected.
Referring to FIG. 2, an alternative or complimentary integrated
circuit utilizing the present invention is shown where modules A
and B have electrical signal inputs 30 and 31, electrical power
inputs 30A and 31A, and electrical outputs 32 and 33, respectively.
Inputs 30 and 31 are connected through load resistors 34 and 35 to
supply bus 36. Electrical power is supplied to the modules through
leads 30A and 31A and preferably through conductive semiconductor
elements as shown in FIG. 1. Conductive semiconductor elements 37
and 38 are the same as conductive elements 17 and 18 described in
connection with FIG. 1 except for differences in electrical
characteristics because of the differences between power and signal
inputs. Conductive elements 37 and 38 are connected to inputs 30
and 31, respectively, by input leads 39 and 40 and by output leads
41 and 42 connected to ground so that inputs of the conductive
semiconductor elements are also connected indirectly through load
resistors 34 and 35 to supply bus 36.
By this arrangement, the circuit modules A and B are selectively
tested by selectively exposing base regions 43 and 44 of conductive
elements 37 and 38 to radiation beam 45 which is preferably the
same radiation beam 27 described above. That is, the conductive
semiconductor elements connected to circuit modules or segments
other than the module or modules to be tested are exposed to the
radiation beam so the input load from the supply bus 36 is shunted
to ground through the exposed conductive elements. This embodiment
is particularly useful in testing logic circuits where the circuit
modules must be tested in both "on" and "off" signal input
conditions.
A difficulty with the use of the embodiments shown in FIGS. 1 and 2
is that usually the power to the entire circuit must be turned off
at the supply bus between the test of each circuit module or
segment. This turn-off permits the thyristor-conductive elements to
return to the nonconductive state so that another circuit module
can be isolated and selectively tested. This turn-off is not
necessary where the conductive elements are transistors or other
types of radiation conductive semiconductor elements that maintain
electrical conductivity only while being irradiated (which provides
an advantage with transistor conductive elements). However, as
pointed out above, the testing time is limited with transistor
conductive elements to the turn-off time of the transistor if
single electron beam is utilized to set all input conditions as
well as accomplish the measurement of the electrical
characteristics of the circuit. Rather, in this embodiment, one or
more light beams will usually be used to selectively maintain the
conductivity of the conductive elements, while the electrical
characteristics of the integrated circuit are measured preferably
with an electron beam. Where thyristor conductive elements are
used, the testing procedure is generally slowed by the need to
turn-off the power supply between each test sequence, and discharge
and recharge the relatively large capacitance of the power supply
bus.
Referring to FIG. 3, a second alternative integrated circuit
utilizing the present invention is shown where the conductive
element can be switched to and maintained in the conductive state
with only a brief exposure to a radiation beam while the need to
turn-off the external power supply between each test is avoided.
Circuit modules A and B of the integrated circuit have electrical
power inputs 50 and 51, electrical signal inputs 63 and 64,
respectively, and electrical outputs 52 and 53, respectively. These
circuit modules are designed to be supplied with electrical power
through leads 54 and 55 from a common supply bus 56; but at the
test stage as hereinafter described, leads 54 and 55 are not yet
electrically connected to the circuit modules. An electrical signal
input is also typically supplied to the modules through leads 63
and 64 from external contact pads or other parts of the integrated
circuit.
Also fabricated as part of the integrated circuit structure are
conductive semiconductor elements 57 and 58 having output leads 59
and 60, respectively, electrically connected to input leads 50 and
51 of circuit modules A and B, respectively. Conductive elements 57
and 58 are electrically connected by input leads 61 and 62 to
common power supply bus 56.
Conductive semiconductor elements 57 and 58 in this embodiment
comprise radiation activated thyristors 65 and 66 and radiation
activated transistors 67 and 68. The thyristor and transistor of
each conductive semiconductor element 57 and 58 are electrically
connected in parallel between the input and output leads. The
thyristors and transistors also have base regions 69, 70, 71 and
72, respectively, of configurations so that the transistors and
thysistors are each capable of exposure by, for example, electron
or light radiation beam 73 of typically fine dimensions.
In this embodiment, the electrical input power to each circuit
module can be selectively turned-off as well as on by the radiation
beam. For example, if circuit module A is to be tested, base region
69 of thyristor 65 would be selectively exposed to radiation beam
73 to cause the thyristor 65 and in turn conductive element 57 to
change to the low impedance conductive state and supply the desired
electrical input signal to the circuit module A at power input lead
50. The circuit module A is then selectively tested by measuring
the current or voltage response in external leads 52 and 56 on
supply of the desired electrical inputs to the module, which
typically includes in addition to the power input, an electrical
signal input through lead 63.
After completion of the test, radiation beam 73 is deflected to
expose base region 71 of radiation activated transistor 67. The
voltage drop through transistor 67 on exposure by the radiation
beam is such that the current is caused to shunt through transistor
67 and cause the current flow through thyristor 65 to reduce below
the holding current and cause the thyristor to resume a high
impedance nonconductive mode. After the radtiation beam is removed
from base region 71, transistor 67 also assumes a nonconductive
state and module A is thus deenergized. Thereafter circuit module B
can be electrically powered and tested by the same procedure
without first turning off the electrical power supply in the
external power bus 56. This embodiment, of course, provides a much
more rapid off technique than deenergizing the entire integrated
circuit because (i) the relatively large capacitance of the power
supply bus does not have to be discharged and recharged for test of
each circuit module and (ii) the radiation beam can be deflected at
high speed to the transistor to turn-off the conductive
element.
Referring to FIG. 4, a third alternative integrated circuit
utilizing the present invention is shown where the desired
electrical power needed at the circuit modules is so large that it
cannot be directly turned off by shunting with a radiation
activated transistor. Specifically, modules A and B have electrical
power inputs 80 and 81, electrical signal inputs 80A and 81A, and
electrical outputs 82 and 83, respectively. Modules A and B are
designed to be electrically connected to and supplied with
electrical power through leads 84 and 85, respectively, from supply
bus 86; but at the test stage as hereinafter described, leads 84
and 85 are not yet electrically connected to the circuit modules.
Again, an electrical signal input is also typically supplied to the
modules through leads 80A and 81A from an external source or other
parts of the integrated circuit.
Fabricated as part of the integrated circuit structure are
conductive semiconductor elements 87 and 88 having output leads 89
and 90, respectively, electrically connected to power input leads
80 and 81 of circuit modules A and B, respectively. Conductive
semiconductor elements 87 and 88 are also electrically connected by
input leads 91 and 92 to the common power supply bus 86.
Conductive semiconductor elements 87 and 88 comprise radiation
activated thyristors 93 and 94, respectively, and electrical gated
transistors 95 and 96 electrically connected in parallel with
thyristors 93 and 94, respectively. Conductive elements 87 and 88
also have diodes 97 and 98, respectively, in series with thyristor
93 and transistor 95 and with thyristor 94 and transistor 96,
respectively, and radiation-activated transistors 99 and 100,
respectively, in parallel, respectively with diodes 97 and 98 and
in series with collector-base portions of transistors 95 and 96,
respectively. Thyristors 93 and 94 and transistors 99 and 100 have
base regions 103, 104, 105 and 106, respectively, of configurations
so that the devices which are normally electrically nonconductive
are adapted to conduct when exposed by radiation beam 107,
typically of light or electrons.
By this arrangement, the circuit modules A and B can be selectively
supplied with the desired high level electrical input power and
possibly other electrical input signals, tested, and thereafter
electrically turned off so that another circuit module may be
selectively tested. For example, circuit module A is selectively
tested by first exposing the base region 103 of thyristor 93 to
radiation beam 107 to cause the thyristor 93 to change from the
nonconductive blocking mode to the conducting mode, and in turn
supply the desired high level electrical input power to the circuit
module A through input lead 80. The circuit module A is then
selectively tested by measuring the current and/or voltage response
in the external input or output leads 82 or 86 to the supply of the
electrical inputs which again typically include in addition to the
power input, an electrical signal input through lead 80A.
After testing, the electrical power input to the module A is
switched off by exposing base region 105 of transistor 99 to
radiation beam 107. Because of the blocking voltage provided by
diode 97, the current is shunted through radiation activated
transistor 99 so that transistor 95 is driven into saturation,
thereby causing the high power electrical input to shunt through
transistor 95 and drop the current flow through thyristor 93 below
the holding current level. Thyristor 93 is thus caused to reassume
its nonconductive blocking mode and, with removal of the radiation
beam from transistor 99, turn off the electrical signal to input 80
of integrated circuit module A. This mode of turn-off of the
thyristor is called a "cascade" turn-off.
The same procedure can thereafter be followed in selectively
supplying electrical power to input 81 of circuit module B, testing
circuit module B typically with additional electrical signal
inputs, and thereafter turning off conductive element 88 by
exposure of base region 106 of transistor 100 with radiation beam
107 and cascade shunting and turn-off of thyristor 94. Similarly,
cascade shunting can also be used in turning "on" and "off"
electrical input signals instead of input power.
Referring to FIG. 5, a fourth alternative integrated circuit is
shown utilizing the present invention in which a plurality of
electrical power inputs at different levels are selectively
supplied to one input of the integrated circuit 109. Integrated
circuit 109 is again preferably of high density built by the
electron image projection technique. The integrated circuit has
electrical power input 110, electrical signal input 110A and
electrical output 111. The integrated circuit is designed to be
supplied with electrical power through lead 112 from power supply
bus 113; but at the test stage as hereinafter described, lead 112
is not yet electrically connected to the integrated circuit. The
circuit is also designed to be supplied with an electrical input
signal from an external circuit or other part of the integrated
circuit through lead 110A.
Also fabricated as part of the integrated circuit structure are
conductive semiconductor elements 114, 115 and 116. Each conductive
element is comprised of radiation activated thyristor 117, and
radiation activated transistor 118 connected electrically in
parallel with thyristor 117. Thyristor 117 and transistor 118 also
each have base regions 119 and 120, respectively, of configurations
so that the devices, which are normally nonconductive, are adapted
to electrically conduct when exposed to radiation beam 121
typically of light or electrons. Beam 121 is preferably a
fine-dimensioned beam projected by a scanning electron microscope
or collimated gas laser, and is adapted to be accurately addressed
and deflected at high speed to various locations within a
relatively large scan field.
Conductive semiconductor elements 114, 115 and 116 also are
comprised of output leads 122, 123 and 124, respectively,
electrically connected to power input lead 110 of the integrated
circuit 109. Conductive semiconductor elements 14, 115 and 116 also
are electrically connected by input leads 125, 126 and 127 through
resistors 128, 129 and 130, respectively, to supply electrical
power to the respective conductive elements from the common power
supply bus 113.
By this arrangement, the electrical signal inputted to the
integrated circuit 109 can be selected by selectively irradiating
one or more of the thyristors of conductive elements 114, 115 and
116 with radiation beam 121. The electrical power inputted to the
integrated circuit at power lead 110 is dependent upon the value of
resistors 128, 129 and 130.
Preferably, the electrical power supply is varied so that the
voltage from supply bus 113 to power input lead 110 remains
substantially constant. In this situation the resistors preferably
have weighted values in the ratios of 1:2:4. That is, resistor 128
has a unit resistance of 1, resistor 129 has a unit resistance of
2, and resistor 130 has a unit resistance of 4. By this weighting
of the resistors relative to each other, the current levels
supplied to the integrated circuit 109 through lead 110 can range
in discrete levels from 0 to 7 times the current level which can be
supplied to input 110 through resistor 128 and conductive element
114. That is, by causing conductive elements 114, 115 and 116 to
electrically conduct in various combinations, the electrical
current level at input 110 can range from 0 to 7 in discrete levels
of 0, 1, 2, 3, 4, 5, 6 and 7. The electrical current level at input
110 can also be changed downwardly simply by irradiating the
appropriate transistor 120 of conductive semiconductor elements
114, 115 or 116 so that the thyristor thereof resumes the
electrical blocking states as explained in connection with FIG.
3.
Referring to FIG. 6, an alternative multi-level signal input
arrangement of the present invention is shown. An integrated
circuit 135 is shown having electrical signal input 136, electrical
power input 136A, and electrical output 137. Signal input 136 is
connected by lead 139 through load resistor 140 to power bus 138.
Semiconductor conductive elements 141, 142 and 143, as described in
connection with FIG. 5, are connected to input 136 by input leads
144, 145 and 146, respectively, and by output leads 147, 148 and
149 to ground so that the electrical inputs of the conductive
semiconductor elements are also electrically connected indirectly
to power supply bus 138. By this arrangement, the input signal to
integrated circuit 135 through input 139 and load resistance 140
can be produced in discrete levels depending upon the values of
resistors 128', 129' and 130'. Again, it may be preferred that the
voltage be maintained substantially constant and the resistors have
related ohmic values according to the ratios 1:2:4. In this way the
multiple current level inputs to integrated circuit 135 relate to
each other, and equally spaced discrete current levels can be
supplied to the integrated circuit 135.
Referring to FIG. 7, still another alternative embodiment of an
integrated circuit made utilizing the present invention is shown.
The integrated circuit, which includes integrated circuit modules A
and B, preferably is again a high density circuit built by use of
the electron image projection system. As part of the circuit
structure, module A is provided with electrical input signal leads
150 and 151 and electrical output lead 152, and module B is
provided with electrical input signal lead 153 and electrical
output lead 154. The modules are designed to be connected by leads
155, 156 and 157; but at the test stage as hereinafter described,
leads 155, 156 and 157 are not yet electrically connected to the
circuit modules.
Also fabricated as part of the integrated circuit structure are
conductive semiconductor elements 159, 160 and 161, each comprised
of a radiation activated transistor and adapted to normally be
nonconductive but capable of electrically conducting on exposure to
a radiation beam. Conductive elements 159, 160 and 161 have output
leads 162, 163 and 164, respectively, electrically connected
through amplifier circuits 165, 166 and 167, respectively, to input
leads 150, 151 and 152, respectively. Conductive elements 159, 160
and 161 also have input leads 168, 169 and 170 to supply electrical
power to the respective conductive elements from the common power
supply bus 158. Conductive elements 159, 160 and 161 also have base
regions 171, 172 and 173, respectively, in close proximity and of
configurations so that the conductive elements can be exposed to
and simultaneously caused to assume an electrical conduction mode
on exposure by a radiation beam 174.
Radiation beam 174 is again preferably a standard fine-dimensioned
beam that is projected by a scanning electron microscope of
collimated gas laser and the beam is preferably accurately
addressed and deflected at high speed to various locations within a
relatively large scan field. The close proximity of the base
regions 171, 172 and 173 to each other permits an electron beam to
be deflected from one base region to the other at a frequency
sufficiently high to bridge the turn-off time of the transistors
and thereby selectively maintain one or more or all of the
transistors in the conducting mode during the testing of the
circuit modules A and B, as desired without the use of a plurality
of radiation beams to maintain all of the input conductions while
the electrical characteristics of the circuit are tested.
For example, an electron beam may be deflected between base regions
171 and 172 of conductive semiconductor elements 159 and 160,
respectively, to provide the desired electrical inputs at inputs
150 and 151 of circuit module A during testing of that module.
Thereafter, the radiation beam can be deflected to base 173 of
conductive element 161 to provide the input at 153 to the circuit
module B for testing thereof.
Amplifier circuits 165, 166 and 167 are provided to boost the
typically small current produced by the incidence of radiation beam
174 on the exposed conductive semiconductor element or elements.
Further, the current gain of the amplifier circuits can be selected
and controlled to provide the desired electrical inputs at inputs
150, 151 and 153.
As previously described, the circuit modules A and B may be tested
by measuring the response or variation in electrical load level of
the power supply 158 because the module being tested is isolated
from the remainder of the circuit. FIG. 7 shows how the accuracy of
this method can be enhanced by use of special low-value load
resistors 175 and 176 of different values. Resistors 175 and 176
are connected between the outputs 152 and 154, respectively, of the
circuit modules A and B and the power supply bus 158. Resistors 175
and 176 are generally 4 to 10 times lower in value than the load
resistance within the respective integrated circuit modules. These
resistors are formed as part of the integrated circuit and
preferably are subsequently disconnected from the integrated
circuit during processing steps subsequent to testing as herein
otherwise described. The presence of resistors 175 and 176 permit
differentiation in the various input and output conditions for
checking desired (or specified) performance. This measurement is
particularly useful in the testing of logic circuit modules with a
relatively small number of gates.
As previously described in connection with FIG. 1, the conductive
semiconductor elements are disconnected from the integrated circuit
after testing. Also, leads and load resistors may be simultaneously
formed to ohmically supply the desired electrical power supply and
electrical signal inputs to and between the various segments and
modules of the integrated circuit. This step is equally applicable
in the processing, after testing, of the embodiments shown in FIGS.
2 through 7.
If a circuit is found on testing to be defective, it is preferably
simply disconnected from the remainder of the integrated circuit
during the subsequent disconnection step along with the conductive
semiconductor elements. In this connection, it is preferred that
the integrated circuit be fabricated with more modules than is
necessary to accomplish the designed purpose of integrated circuit.
In this way, the yield of the integrated circuit can be increased
-- in some cases, e.g. computer memories, to almost 100% -- by
accommodation and passivation of the defective circuit segments and
modules within the finished integrated circuit. This is readily
done, after testing of all of the circuit segments and modules,
with a computer-derived photomask or electromask which will permit
connection of the good modules and/or disconnection of the
defective modules by known lithographic and etch techniques. It
should also be noted in this connection that any defects in the
conductive semiconductor elements are preferably treated as a
defect in the integrated circuit segment or module under test to
eliminate the need for testing the conductive elements before the
testing of the integrated circuit; this preference is accomplished
simply by inclusion of sufficient redundancy into the integrated
circuit that the probable defects in the conductive semiconductor
elements can be accommodated and passivated.
While the presently preferred embodiments have been shown and
described with particularity, it is distinctly understood that the
invention may be otherwise variously performed within the scope of
the following claims.
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